1. Field of the Invention
The present invention relates to a distortion compensating apparatus and a compressed data generating method, for example, a distortion compensating apparatus which may be suitably applied to a transmitting apparatus of a radio base station to be used for a mobile communication system.
2. Description of the Related Art
A radio base station used in the mobile communication system is provided with a distortion compensation apparatus for reducing distortion generated in a power amplifier in order to transmit a high power signal to mobile stations.
As the distortion compensating system, various methods have been proposed and a predistortion system is one example of such methods.
The predistortion system has been proposed to reduce distortion of the amplified signals by providing an inverse distortion characteristic for the distortion generated in the amplifier to the signal before input to the amplifier.
Here, since distortion generated in the amplifier changes in accordance with the input signal (particularly, input signal level), it is preferable that a coefficient (distortion compensation coefficient) for providing inverse distortion is specified by the input signal level and the input signal is then compensated on the basis of this coefficient.
Therefore, in the predistortion system, a look-up table (LUT) for storing the distortion compensation coefficients corresponding to the addresses generated from the input signal is used.
For this look-up table, the coefficients are written at high speed with an exclusive circuit considering activation of power supply and reset thereof as a trigger and all coefficients are completely set before start of operation.
Japanese Unexamined Patent Publication No. 2001-267850 discloses predistortion.
According to the background of the invention described above, the look-up table (LUT) of the distortion compensation apparatus is triggered by activation or reset of the power supply to write at a high speed the coefficients with the exclusive circuit.
However, when a large amount of distortion compensation coefficients are required to be written, a longer time is required until the completion of write. Particularly when it is attempted to perform the write process using a processor without use of the exclusive circuit, the distortion compensation coefficients must be read in the sequence of addresses for the write process. In this case, additional time is required.